The present invention relates generally to protective hardware for electrical systems and more particularly to a safety device for tagging and preventing closure of a knife switch in a terminal block.
Lockout and tagout (LOTO) procedures are used in industry and other operational settings to ensure that machinery and electrical circuits are shut off or isolated to facilitate safe maintenance, grooming, testing troubleshooting and other servicing work. It requires that power sources to a system or machine be isolated or rendered inoperative before any procedure is conducted on the system or machine. Ideally, a LOTO procedure includes measures for (1) assuring that the system or machine cannot be accidentally or inadvertently reconnected to its power source(s) (the “lock-out” function) and (2) providing readily apparent visual or other evidence of the unpowered status of the system or machine and/or the device used to accomplish this status (the “tag-out” function).
Some systems, however may not lend themselves to a lock-out function because the switches used to isolate circuitry cannot be easily locked in their unpowered positions. This leads to the undesirable situation where safety would have to depend entirely on tag-out procedures.
In most operational settings, LOTO procedures are required to meet government safety standards. In the civilian arena these are typically established by OSHA. In the military setting, the standards and procedures may be set by the service branches. See, e.g., the U.S. Navy's Tag-Out Users Manual, NAVSEA 50400-AD-URM-010/TUM Rev. 6 (“Navy TUM”), which sets forth Navy requirements and is incorporated herein by reference in its entirety. Such requirements will often discourage or prohibit tag-out-only safety procedures as in the following Navy requirements:                4.c. . . . A Danger tagged switch shall not normally be used for electrical isolation or as a single means for preventing operation. If the circuit requiring isolation cannot be de-energized by other means, e.g., opening circuit breakers or removing fuses, without significantly affecting current operational requirements, a tagged switch may be used except as prohibited in paragraph 4.c.(1). In addition to danger tagging required circuit breakers and/or fuse holders, tags may also be attached to a switch to indicate that the associated circuit is danger tagged, and to prevent inadvertent operation of that switch.                    (1) Use of a tagged switch for electrical isolation or as a single means for preventing operation is expressly prohibited in the following cases:                            (a) The switch's physical location makes it subject to inadvertent operation.                                                Navy TUM, Appendix F, Sec. 4.c        